Centrifugal compressors have a wide variety of industrial and aeronautical applications, including gas turbine engines, fluid pumps and air compressors. Centrifugal compressors generally consist of at least two main components: an impeller and a diffuser.
Pipe diffusers, generally having circumferentially spaced frustro-conical discrete passages, are commonly used to perform these functions. Typically, the radially extending passages are angled from the radial direction such that their center lines are all tangent to a single tangency circle. A partially vaneless space is therefore created where the passages intersect, between the tangency circle and an outer leading edge circle. The intersection of circular pipe diffuser passages creates symmetrically located elliptical leading edge ridges formed on the leading edge circle. When such a diffuser is placed around an impeller, the exit flow from the impeller will enter the diffuser at the tangency circle, flow through the partially vaneless space, and enter the discrete passages of the diffuser.
One cause of centrifugal compressor pressure losses, which negatively affect the compressor efficiency and therefore the overall compressor aerodynamic performance, is any mismatch between the impeller exit flow angles and the inlet angles of the diffuser. As the distribution of the impeller fluid exit angles from the impeller hub to the shroud end of the impeller vanes is not uniform, it follows that ideally the leading edges of the diffuser passages would be shaped to provide a corresponding profile of inlet angles. Traditionally used diffuser pipes having a circular cross-section form generally oval diffuser passage leading edges, which fail to provide such an ideal match with the impeller fluid exit angles.